The present disclosure relates to electronic technology, and more particularly to substrates used to connect semiconductor integrated circuits to each other and to other circuits.
Integrated circuits (ICs) have tiny, closely-positioned contact pads that are difficult to connect to other circuits because the contact pads can be shorted to each other (by solder for example), can be misaligned with the other circuits due to warpage of circuit structures, and can be broken off from the other circuits by stresses arising from thermal expansion.
The ICs and other circuits can be interconnected through a common substrate such as a multi-layer ceramic interposer 110 (FIG. 1A) of the kind described in U.S. Pat. No. 7,833,370 issued to Kawamura et al. on Nov. 16, 2010. In FIG. 1A, ICs 120 have contact pads 120C attached to contact pads 110C of interposer 110 by connections 124 which may be solder, adhesive, or some other type. Interposer 110 includes conductive lines that interconnect the contact pads 110C in a desired pattern. The conductive lines include horizontal conductive lines 110LH and vertical conductive vias 110LV. In this example, interposer 110 has contact pads 110C both on top and bottom; the bottom contact pads can be connected to another substrate such as a printed circuit board (PCB) 114, by connections such as 124′. We call substrate 110 an “interposer” because it has contact pads both on top and bottom. In the past, the term “interposer” was used if contact pads 110C were differently spaced on top than the bottom: the top contact pads 110C can be closely-spaced to match the ICs' miniature spacings between pads 120C, while the bottom contact pads 110C can be farther apart to match coarser fabrication technology such as used for PCBs. However, in more recent use, the term “interposer” can denote any substrate used to interconnect other circuits and having contact pads both on top and bottom.
The interposer 110 of FIG. 1A has two layers 110.1, 110.2. FIG. 1B is an exploded perspective view of the two layers, and FIG. 1A shows a cut-away view obtained by cutting away the front part of the interposer by a vertical plane A-A (parallel to the XZ plane of an orthogonal XYZ coordinate system). The interposer is shown in a horizontal position, i.e. extending along a horizontal XY plane. Each layer 110.i (110.1, 110.2) includes a ceramic sheet 110S extending horizontally. In each layer 110.i, the horizontal lines 110LH are on top of the ceramic sheet, and vertical vias 110LV pass through the ceramic sheet to connect the horizontal lines 110LH to underlying features. The vertical vias 110LV are formed by punching holes in the “green” ceramic (i.e. before the ceramic is fired) and filling the holes with a conductive paste.